JP2002509295A - Method for reducing charge accumulation in field emission displays - Google Patents

Abstract

SUMMARY OF THE INVENTION A method for reducing charge accumulation in a field emission display (100) is to cause a plurality of electron emitters (114) to emit electrons (132) so that the anode (124) of the field emission display (100). And reducing the potential at. As the potential is reduced at the anode (124), the electrons (132) neutralize the positively charged surface (129) of the spacer (130). The anode potential is reduced by providing a resistor (127) placed in series with the voltage source (126) in connection with the anode (124). The anodic potential is reduced by causing the electron emitter (114) to simultaneously emit electrons and generating a pull-down current (128) at the anode (124). The voltage at the anode (124) is reduced to a value that attracts sufficient electron (132) flow to the charged surface (129) to cause neutralization.

Description

DETAILED DESCRIPTION OF THE INVENTION

FIELD OF THE INVENTION The present invention relates generally to field emission devices, and more particularly to a method for reducing charge accumulation in a field emission display.

BACKGROUND OF THE INVENTION Field emission displays are well known in the art. They include an anode plate and a cathode plate that define the boundaries of the thin envelope. In general, the anode and cathode plates need some form of spacer structure to prevent the device from bursting due to the pressure difference between the internal vacuum and the external atmospheric pressure, and are therefore thin enough. ing. The spacer is located within the active region of the device and includes an electron emitter and a phosphor.

[0002] The potential difference between the anode plate and the cathode plate is typically in the range of 300 to 10,000 volts. To withstand the potential difference between the anode and cathode plates, the spacer typically includes a dielectric material. As such, the spacer has a dielectric surface that is exposed inside the vacuum of the device.

[0003] During operation of a field emission display, electrons are emitted from an electron emitter such as a Spindt chip on a cathode plate. These electrons traverse the vacuum area and impinge on the phosphor. Some of these electrons can strike the dielectric surface of the spacer. In this way, the dielectric surface of the spacer is charged. Usually, the dielectric spacer is positively charged because the amount of secondary electrons generated by the spacer material is initially two or more.

[0004] The charging of dielectric surfaces in field emission displays creates a number of problems. For example, control over the trajectory of electrons near the spacer is lost. Also, the risk of arcing events increases dramatically.

[0005] Therefore, a need exists for a method of reducing charge accumulation in a field emission display.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For simplicity and clarity of illustration, the elements shown in each figure are not necessarily drawn to scale. For example, the dimensions of some elements are relatively large. Furthermore, where deemed necessary, these figures show the same elements,
The same reference numbers have been used repeatedly.

[0007] The present invention is directed to a method of reducing charge accumulation in a field emission display. The method of the present invention comprises the steps of causing the electron emitter to emit electrons and adjusting the controllable potential in the display so that the potential of the positively charged surface can attract the emitted electrons to the charged surface. Including the step of In this way,
Positively charged surfaces are neutralized. In a preferred embodiment, the field emission display comprises:
In operation, it has a positively charged spacer. To neutralize this charge, the high positive potential of the anode plate is reduced at the end of each frame time. The anode potential is lowered by first providing a resistor in series with the anode voltage source. The anode potential is reduced by causing all electron emitters to emit electrons simultaneously, creating a pull-down current at the anode. The resistance of the resistor is selected to produce a useful anode voltage drop for a given pull-down current value. The voltage drop is such that some of the emitted electrons are attracted to the positively charged surface, thereby dropping enough to neutralize the surface.

FIG. 1 is a cross-sectional view of a field emission display 100 according to an embodiment of the present invention.
The field emission display 100 includes a cathode plate 110 and an anode plate 122. The cathode plate 110 includes a plurality of electron emitters 114, which are formed on a substrate 111. The substrate 111 is made of a dielectric material such as glass and silicon. Cathode plate 110 further includes a plurality of rows and a plurality of columns for selectively addressing electron emitters 114. The rows and columns are made from a suitable conductive material.

For ease of understanding, FIG. 1 shows several rows (rows 115, 116, 117, 118, 1).
19, 120) and only one column (column 112). However, it should be understood that any number of rows and columns can be employed. A typical field emission display 100 has 240 rows and a typical number of columns is 720.

The column 112 is disposed on the substrate 111, and the dielectric layer 113
Formed on The dielectric layer 113 defines the boundary of the well in which the electron emitter 114 is located. Rows 115, 116, 117, 118, 119, 120
Is formed on the dielectric layer 113. Matrix addressable (addressabl
e) Methods of making cathode plates for field emission displays are known to those of ordinary skill in the art.

The anode plate 122 includes, for example, a transparent substrate 123 made of glass. The anode 124 is
It is arranged on the substrate 123. The anode 124 is made of indium tin oxide (indium tin oxide).
Made from transparent conductive material such as n oxide). In a preferred embodiment, anode 124 comprises
It is a continuous layer facing the entire dischargeable area of the cathode plate 110. That is, the anode 124 faces the entire electron emitter 114. The anode plate 122 further includes a plurality of phosphors 125, the phosphors being made from a cathodoluminescent material and disposed on a substrate 123. Methods of making anode plates for matrix-addressable field emission displays are also known to those of ordinary skill in the art.

The field emission display 100 further includes a frame 121 and a plurality of spacers 130.
, All of which are located between the anode plate 122 and the cathode plate 110.
The frame 121 and the spacer 130 help maintain a separation distance between the cathode plate 110 and the anode plate 122. In the embodiment shown in FIG.
And a rectangular structure circumscribing the active region of the anode plate 122 and the active region of the anode plate 122. For clarity, only one spacer 130 is shown in FIG. The actual number of spacers is
Depends on device structural requirements.

The spacer 130 is made from a dielectric material. Spacers 130 can also be thin plates / ribs of dielectric material. Also, each spacer 130 can include multiple elements, some of which are dielectric. For example, each spacer 130 can include a layer of various materials, at least one of which is dielectric. The dielectric material defines one surface, which becomes a positively charged surface 129 during operation of the field emission display 100. Other surfaces within the field emission display 100 may also become positively charged during operation of the device. The method of the present invention also helps to reduce the charge on these surfaces.

The voltage source 134 is connected to the column 112 by applying an appropriate voltage to the column 112 as defined by the display data. Voltage source 126 is connected to anode 124. In the preferred embodiment, voltage source 126 is a direct current (DC)
Voltage source. In the preferred embodiment, resistor 127 includes a voltage source 126 and an anode 124.
Are connected in series. Row drivers (not shown)
17, 118, 119, and 120. The row drivers are rows 115 and 116
, 117, 118, 119, 120 to generate a display image and reduce the accumulation of charge in the field emission display 100 according to the present invention.

Here, the operation of the field emission display 100 will be described with reference to FIG. 1 and FIG. FIG. 2 is a timing diagram 200 illustrating a method for reducing charge accumulation in a field emission display 100 according to the present invention. The timing diagram 200 shows a row driver timing graph 210 and an anode voltage response graph 220. The anode voltage response graph 220 represents the voltage at the anode 124.

The operation of the field emission display 100 is characterized by a series of repeated steps. One of these cycles is called a display frame. In accordance with the present invention, each cycle includes a display time represented by timing diagram 200 between times t ₁ and t ₂ , and a charge reduction time represented by timing diagram 200 between times t ₀ and t ₁ . .

During display time, voltage source 126 provides a potential of _VA and attracts a plurality of electrons 132 to anode 124. The potential of anode 124 is below the potential provided by voltage source 126 due to the voltage drop across resistor 127. The potential _{VA of the} anode 124 desirably exceeds 600 volts. More preferably, the anode potential V _A exceeds 1000 volts. Most preferably, the anode potential V _A is greater than 3000 volts. For example, the potentials applied to the rows and columns to cause emission can be on the order of 80 volts and ground potential, respectively.

During the display time, rows 115, 116, 117, 118, 119, 120 are sequentially scanned by row drivers (not shown), simultaneously with the step of generating a positive potential at anode 124, as described above. You. By scanning, a potential suitable for causing electron emission is selectively applied to the scanned row. Whether each electron emitter 114 in a scanned row emits electrons depends on the display data and the voltage applied to each column. Electron emitters 114 in unscanned rows do not emit electrons. During the display time, a display image is generated on the anode plate 122 and the exposed dielectric surface within the field emission display 100 can be positively charged by static electricity. For example, in the embodiment of FIG. 1, the dielectric surface of spacer 130 is a positive electrostatic charging surface 129.

The spacer 130 is charged because part of the electrons 132 collides with the spacer 130 without reaching the anode 124. Since they have more than one secondary electron emission, the surface of spacer 130 emits more than one electron for each electron received. Therefore, a positive potential is generated at the spacer 130.

According to the present invention, the positively charged electrostatic surface 129 is neutralized during the charge reduction time, as shown in FIG. In the preferred embodiment, the charge reduction time occurs at the end of the display frame. However, other suitable timing schemes can be used.
For example, the charge reduction phase may be performed after multiple row scanning cycles have been performed.
It can also be implemented.

During the charge reduction time, in accordance with the present invention, the entire electron emitter 114 causes the emission of electrons by applying an appropriate emission “on” potential to all rows and columns of the cathode plate 110. The step of causing all the electron emitters 114 to emit electrons results in a pull-down current 128 at the anode 124, as shown in FIG. During the stage of causing all electron emitters 114 to emit electrons, voltage source 126 is not switched.

In general, the value I of the pull-down current 128 and the resistance R of the resistor 127 are to a value sufficient to allow some of the electrons 132 to be attracted by the potential of the positively charged electrostatic surface 129. , Is selected to reduce the positive potential of the anode 124. In the preferred embodiment, all electron emitters 114 emit electrons during the charge reduction time. Thus, the electron current available for both neutralization and generation of the pull-down current 128 is equal to the product of the total number of rows and the maximum emission current per row. Resistor 127
, The voltage at the anode 124 drops significantly. As the voltage drops, the electrons 132 are increasingly attracted to the positively charged electrostatic surface 129, reducing the portion of the emission current that reaches the anode 124.

Finally, an equilibrium state is established. In the equilibrium state, part of the emission current is
24, creating a voltage drop across resistor 127. As shown in FIG. 2, the equilibrium voltage V _e is realized at the anode 124. The value of the reduced voltage is considered to be slightly higher than the row voltage. The remainder of the emission current is attracted to the positively charged surface, such as positively charged surface 129, causing neutralization.

Adjusting the potential of the anode 124 includes reducing the potential of the anode 124 to a value sufficient to achieve a flow of electrons at the positively charged electrostatic surface 129, which involves neutralizing the charge. Help to sum. The length of the charge reduction time is selected to be sufficient for the required neutralization of the surface 129 and not to distort the display image. After completion of the charge reduction time, the next display frame is started by another row scanning cycle.

The embodiments of FIGS. 1 and 2 provide a number of advantages. For example, there is no need to switch the anode potential source, and the duty cycle is low, so that the required power is low.

According to the present invention, the controllable positive potential in the field emission display 100 can be adjusted to a value that helps neutralize the charge at the positively charged electrostatic surface. In the example of FIG. 1, the electrons 132 are used both to adjust the potential at the anode 124 and to neutralize the charge at the positively charged electrostatic surface. In general, the method of the present invention is not limited by the way the controllable positive potential in the display is adjusted. It is further understood that the anode potential can be reduced to an appropriate value by having less than all of the electron emitters emit electrons. For example, electrons can be emitted only to the electron emitter closest to the spacer.

FIG. 3 is a block diagram of a row driver 300 according to a preferred embodiment of the present invention. FIG.
As shown, the plurality of output drive signals 350 of the row driver 300
, 116, 117, 118, 119, and 120, respectively. Output drive signal 350 helps control electron emission at electron emitter 114. During the display time (FIG. 2), only one of the output drive signals 350
It has a potential that is useful to cause release. During the charge reduction time (FIG. 2), each of the output drive signals 350 has a potential that is useful to cause an emission.

The row driver 300 includes a scanning logic circuit 310, a gate logic circuit 320,
It has a level shifter circuit 330 and an output driver 340. Scanning logic 310 receives clock signal 312 and seed 314. Scanning logic 310 functions as a shift register to move incoming display data.

The output 316 of the scanning logic 310 is sent to the gate logic 320, which controls the asynchronous and simultaneous modes of row activation. Control signal 31
7 is provided to the gate logic 320, resulting in simultaneous activation of all rows.
The blanking signal 318 is provided to the gate logic circuit 320 and is used to turn off the output of the row driver and disable all other signals. The polarity signal 319 is
It is provided to gate logic circuit 320 and controls the magnitude of output drive signal 350. A plurality of other signals 321 such as a clock signal and a seed are provided to the logic circuit 320 to control the operation.

The plurality of outputs 322 of the gate logic circuit 320 are sent to a level shifter circuit 330, which produces a plurality of outputs 323. Level shifter circuit 330 converts the low level signal to a useful level. Output driver 340 is an analog device that generates an appropriate value of output drive signal 350.

One of ordinary skill in the art will appreciate that the order of the steps of the methods described herein can be varied as needed.

The present invention is directed to a method for reducing charge accumulation in a field emission display. The method of the present invention causes the electron emitter to emit electrons and adjusts a controllable potential in the display so that the potential of the positively charged surface attracts the emitted electrons to the charged surface. Includes the step of: In this way, the positively charged surface is neutralized. In a preferred embodiment, the high positive potential at the anode is reduced by causing the electron emitter to emit electrons, resulting in a pull-down current at the anode. The anode potential is reduced by providing a resistor in series between the DC voltage source and the anode. The method of the present invention does not require switching of a voltage source connected to the anode. Preferably, the DC voltage source provides a potential greater than 600 volts,
It is more desirable if the potential is above 1000 volts, most preferably above 3000 volts, and switching at such high voltages may be otherwise difficult, so that switching of the voltage source is unnecessary. Is an advantage.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a field emission display according to an embodiment of the present invention.

FIG. 2 is a timing diagram illustrating a method for reducing charge accumulation in a field emission display according to the present invention.

FIG. 3 is a block diagram of a row driver according to a preferred embodiment of the present invention.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Chengan Zi West Cathedral Rock Drive, Phoenix, Arizona, USA 1736 F-term (reference) 5C032 AA01 CD06 5C036 EF01 EF06 EG02 EG50 5C080 AA08 AA18 BB05 CC03 DD09 DD30 FF07 HH17 JJ04 JJ06

Claims (10)

[Claims] 1. A method for reducing charge accumulation in a field emission display, comprising: generating a controllable positive potential in the field emission display; and a positive electrostatic charge in the field emission display. Providing a surface; causing an electron emitter in the field emission display to emit electrons;
Adjusting the controllable positive potential so that electrons are received by the positive electrostatic charging surface, thereby neutralizing the positive electrostatic charging surface. A method characterized by the following. 2. The method according to claim 1, wherein the step of adjusting the controllable positive potential is performed simultaneously with the step of causing the electron emitter to emit electrons. How to reduce. 3. The field emission display according to claim 1, wherein the step of generating a controllable positive potential comprises the step of generating a controllable positive potential greater than 600 volts. A method to reduce charge accumulation. 4. The step of generating a controllable positive potential comprises generating a controllable positive potential greater than 1000 volts.
4. A method according to claim 3 for reducing charge accumulation in a field emission display. 5. The step of generating a controllable positive potential comprising generating a controllable positive potential greater than 3000 volts.
A method for reducing charge accumulation in a field emission display according to claim 4. 6. A method for reducing charge accumulation in a field emission display, comprising: generating a positive potential on an anode of the field emission display; and forming a positive electrostatically charged surface in the field emission display. Providing; emitting electrons to an electron emitter in the field emission display;
And reducing the positive potential at the anode enough to allow electrons to be received by the positive electrostatically charged surface, thereby neutralizing the positively electrostatically charged surface. A method comprising: 7. The step of causing the electron emitter in the field emission display to emit electrons comprises the step of causing the electron emitter in the field emission display to emit electrons to provide a pull-down current at the anode. The step of reducing the positive potential of the anode includes the step of providing a resistor arranged in series with a voltage source so as to be connected to the anode, and the step of reducing the resistance of the resistor and the value of the pull-down current. 7. The charge accumulation in a field emission display according to claim 6, characterized in that the charge is selected to drop to a value sufficient for electrons to be received by the positive electrostatic charging surface. How to reduce. 8. The method of causing the electron emitters in the field emission display to emit electrons comprises simultaneously emitting electrons to the entire electron emitters in the field emission display. A method for reducing charge accumulation in a field emission display according to claim 6. 9. The step of providing a positively charged electrostatic surface in the field emission display comprises the step of providing a spacer between a cathode plate and an anode plate in the field emission display. 7. A method for reducing charge accumulation in a field emission display according to claim 6. 10. The method of claim 6, wherein the method of reducing the positive potential of the anode comprises reducing the positive potential of the anode at the end of each display frame. , A method of reducing charge accumulation in a field emission display.